There was a significant increase of IL-17(+) cells infiltrating the liver of NASH patient and increased gene expression of Th17 cell-related cytokines (IL-17, IL-21, and IL-23). Hepatic Th17 cells and IL-17 were associated with steatosis and pro-inflammatory response in NAFLD and facilitated the transition from simple steatosis to steatohepatitis. This evidence concerns the gene IL17A and metabolic dysfunction-associated steatohepatitis.